Most rear-end collisions are generally caused by, after a front vehicle involved in an accident or breakdown, advance-warning not being promptly given, which causes the vehicles behind to rear-end the vehicle in front. The rear-end collisions are also caused by the poor visibility and closeness to the accident scene of the warning equipment of the vehicle involved in the accident, the vehicles following do not have sufficient time or distance to respond. Thus, as required by transportation authorities, after a road accident, an advance-warning device must be used to warn the vehicles behind, at a distance of 100-250 meters. However, when a warning device is manually placed, safety of workers would also be threatened by vehicles passing by. Therefore, a warning device that can be self propelled would be beneficial.